The present invention relates to improvements in grates for industrial furnaces or the like, and more particularly to improvements in grates wherein mobile grate bars alternate with stationary grate bars. Still more particularly, the invention relates to improvements in grates of the type wherein mobile grate bars are coupled with but can be displaced relative to the adjacent stationary grate bars.
German Pat. No. 911,317 discloses a grate wherein each step comprises mobile and stationary grate bars. The mobile grate bars have laterally extending hook-shaped projections which extend through openings provided in the adjacent flanges or ribs of stationary grate bars. The projections overlie the inner sides of the respective ribs to establish connections between the mobile and stationary bars. The openings in the ribs are elongated slots which enable the mobile grate bars to perform requisite movements with respect to the adjacent stationary bars.
A drawback of grates which are disclosed in the aforementioned German patent is that the clearances between stationary and mobile grate bars cannot be selected and maintained with a requisite degree of precision. This is due to the fact that the stationary grate bars are normally produced by casting or forging and the inner sides of their ribs are not machined or otherwise treated so that the distance (i.e., the width of clearances) between neighboring stationary and mobile grate bars varies in response to sliding movement of projections along the normally uneven inner sides of adjacent ribs forming part of the stationary grate bars. Another reason for continuous or intermittent variations of the width of clearances between stationary and mobile grate bars is that the mobile grate bars including the aforementioned hook-shaped projections, too, are not machined with a high degree of precision. During movement of mobile grate bars with respect to neighboring stationary grate bars, rough (i.e., untreated) surfaces of mobile bars slide along similarly untreated surfaces of stationary grate bars which results in pronounced friction and extensive wear upon stationary and mobile bars. The wear is especially pronounced upon the projections whose dimensions are relatively small (the width of such projections is normally in the range of 20 millimeters) so that the projections wear away and the width of clearances between the mobile and stationary grate bars increases accordingly. As the width of clearances increases, the dimensions of solid particles which penetrate or can penetrate between the mobile and stationary grate bars also increase; this can affect the length of strokes which are performed by mobile grate bars and can also result in jamming of the grate. If several mobile grate bars are held against movement at one and the same time, the mechanism which reciprocates or otherwise moves the mobile bars is likely to be damaged or destroyed or to be incapable of effecting any movements of the grate and/or grate bars. The situation is aggravated if the width of clearances increases at both sides of a given mobile grate bar; the frictional force which is generated by relatively large solid particles of foreign matter between the stationary grate bars and the mobile bar then increases to such an extent that the mobile bar invariably comes to a full stop. Jamming can be caused by particles of rock, stone, clinker and/or metallic parts which are contained in the fuel, e.g., in refuse if the grate is used in an incinerator plant.